texts: Determining line ratios in planetary nebula

texts: I know that the line strength ratio tells us how hot the electron plasma in a nebula is, and also give information about the electron densities in the nebula. But how do you compute the line ratios? Say we consider two emission lines (both forbidden) decaying to the ground state. If I have the Einstein A coefficients and the statistical weights, how do I compute the line ratios? Any explanation (preferably with examples) will be highly appreciated.


texts: Could asteroid mining affect gravitational balance?

texts:
I'm just a guy who is interested in all topics around space, so forgive me if it is a dumb question.

I have read some things about asteroid mining in the past and I think it's a really interesting topic, as it opens up a lot of possibilities.

But one thing came to my mind. Humans tend to pushing things a little too far sometimes when we want to reach a goal. So, imagine, we are getting really good at off-earth mining at a larger scale and in a larger timespan, we continue to mine thousands and thousands of asteroids. Wouldn't that affect the gravitational balance of our star system at some point, or is the gravitational influence of an asteroid belt negligible? I am talking about extreme examples, like removing nearly the whole asteroid belt beyond Mars. Also, what would happen to all the stuff we don't need from an asteroid?

I'm sure I'm not the first one who thinks of something like this, but I found nothing about this particular topic.


texts: Sample bias' contribution to "Planet 9" hypothesis, why was this not thoroughly addressed before?

texts:
Science Claim for giant 'Planet Nine' at Solar System's edge takes a hit
arXiv No Evidence for Orbital Clustering in the Extreme Trans-Neptunian Objects

The brightness of distant solar system objects varies as $1/r^4$ and so for elliptical orbits objects are more likely to be discovered near periapsis.
If discovery telescopes are pointed in a biased direction, resulting discoveries will show a bias in orbital elements due to this pointing bias.
That's a rough summary of the recent paper.
Question: Why was this sample bias not thoroughly addressed before? Was there perhaps insufficient statistics until now for such an analysis, or were there other complicating factors?


texts: Can I do M.Sc in physics to become an astronomer after doing B.Tech in aeronautical engineering?

texts:
I am a student of class 12 and I am studying in India. I want to be an astronomer and I know that I have to get a B.Sc, then M.Sc, and then Ph.D in astronomy. I have also started to learn the python programming language. I came to know that there are less opportunities for research in astronomy, since many organizations like ISRO not only employ scientists, but also employ engineers to make satellites and spacecrafts. I will try my best to become an astronomer, but to have life security (if i am unemployed), can I do aeronautical engineering so that I can even get employed in ISRO? After having a degree in engineering and after doing engineering can i do M.Sc in physics and then i start preparing to be an astronomer?

Let me tell you about myself a bit, I love to study science and I love to learn about stars (I have also watched documentaries on astronomy like "How the universe works" and "Cosmos"). I also love aircraft so aeronautical engineering would also be a job that I would love. And please tell me should I also do some extra courses which would enhance my skills as an astronomer?


texts: How many science instruments can be used in parallel with the Hubble Space Telescope?

texts:
The Hubble Space Telescope offers a parallel obervation mode. Observing programmes such as CANDELS and CLASH use WFC3 and ACS in parallel fields. These are also the only instruments of which I have heard that they are being used in parallel. Here are my questions:

Is it possible to observe with more than two instruments in parallel? If so, what is the limit, and why?

Why aren't all observations done with as many instruments as possible turned on?  Granted, a lot of the data would be useless / difficult to analyze (like spectra of a random patch of sky), but on the other hand it might lead to serendipitous discoveries. HST won't last forever, so why not get the most use possible out of it?

Note that this is about the science instruments - I assume the guidance sensors will be working alongside the others anyway. (Or is that wrong?)


texts: If sometime in the distant future, the Universe stopped expanding, would this mean that the Universe was no longer infinite?


texts: When a star reaches the red giant phase, why does it become more opaque?

texts:
Please refer to this answer from Quora:

  ... a star will become a red giant before it begins burning helium. In fact, it will bloat into a red giant while still burning hydrogen in a shell on the surface of the helium core. Shell burning, however, does release more energy than core-burning, but even that alone wouldn’t cause the star to become a red giant, since it could just shine brighter. The real culprit is the combination of the higher energy production rate AND that the star has a higher opacity at that stage in life. This produces an energy crisis where the energy cannot escape radiatively fast enough, and convection would have to be supersonic to rebalance the star. Since supersonic convection is highly disfavored (i.e. impossible), the star greatly expands to the point that the energy flux at the burning shell matches the energy flux at the now much larger surface again.

This is one of the best explanations I've found for how stars transition to red giants. However, the section I've bolded is confusing to me: why would the star become more opaque, and what causes that to occur?


texts: Where to find, if it is possible, values of the mass and the distance of HD 51684, please? Many thanks.


texts: Do we know at which angle the Event Horizon Telescope will look at the accretion disk of Sagittarius A*? Additionally, would it matter if we are exactly in the plane with the accretion disk, i.e. could we still observe the event horizon?


texts: How did Michelson measure the diameters of jupiter's moons using optical interferometry?

texts:
In Betelgeuse: How its Diameter was measured (Chant, C. A., Journal of the Royal Astronomical Society of Canada, Vol. 15, p.133, Bibliographic Code: 1921JRASC..15..133C) the author says:

The paper in which this result was given was published in the Philosophical magazine  in 1890, and in it Michelson remarks that the method might be used in measuring the diameters of small planets, satellites and possibly the fixed stars. Next year, by invitation of Lick Observatory, he tested his method on the satellites of Jupiter with decided success, his results being near to the mean of the measurements made by astronomers with the micrometer. (See Michelson, Light-Waves and their Uses, p. 142.)

This article is on pages 133-136 and I assume this means that I should turn several pages forward and look for Light-Waves and their Uses staring on page 142, but alas I'm not in a library, enjoying "old book smell" and leaving through 100 year old journals.
I've tried several internet attempts to search for a link, and edited the url to the current article to try to move to page 142, but nothing works.
Question: How did Michelson measure the diameters of jupiter's moons using optical interferometry, and how can I read further about it? What instrument did he use, what slit spacings, etc?
Related, describing what the article linked above describes: What equipment and techniques were used to study Betelgeuse's diameter in 1920?


texts: Our universe the surface of a 4-dimensional sphere?

texts: The cosmic microwave background that we observe uniformly around us is usually explained by assuming that our universe is the surface of a four dimensional sphere. That way the uniformity makes sense since there is no center. My question is if this is true then what is the explanation that describes the fact that the farther we look into space, the further we look back in time. I can't perfectly picture this and see how it would coexist. Help me out.


texts: A question about calculating the radius of a comet

texts:
A Comet is orbiting around the sun with period of $T= 5.5$ years. The comet has radius $R$. After 5.5 years (A period) we understand that its radius has decreased about $20cm$. How can we calculate the R. We know that comet is approximately a sphere and it is made of Ice. We have the $G = 6.67 * 10^{-11}$ SI_Unit, $M_{sun} = 1.99 * 10^{30} Kg$, $\sigma = 5.67 *10^{-8}$ SI_Unit (Stefan-Boltzmann constant) , $L_{sun}=3.85 * 10^{26} w$, $l_f = 333 KJ/Kg$ , $l_v = 2260 KJ/Kg$. It would be fine that if the solution doesn't need the numerical value of density of ice but if it can't be solved without density of ice, you are allowed to use it.

I can calculate the distance to sun ($a$) with formula:
$T^2 = 4 *\pi^2 a^3 /(GM_{Sun})$.

$a= 4.66* 10^{11} m$

I also can calculate $F= L_{sun} / (4 * \pi * a^2)$.

I also approximated the power that the comet gives is: $P = F * Area$ (think ice don't reflect any light)

But I don't know how to calculate the R and formulate how it decreases every moment (because it affects the area).


texts:
What we can assume by the shape of universe. As I know when we talk about universe we talk about multi dimension structure but that structure should have some shape. I wonder that if we look the Universe from a far distance, how it will look like?
I know people will tell that its infinite we can't go outside universe and see, but assume if its true that universe has some end and its too far and out of our reach due to our limitation but exists.
I feel that its a kind of myth or assumption that universe is infinite everything is finite in this universe.
Do you remember in early times around 1000 years before humans used to think that earth is flat and infinite?
But after many years we reach to conclusion that earth is round.
Don't you think we are misunderstanding universe the same way we did before for Earth?


texts: Could I create a staircase to the moon and walk to it?

texts: Assuming one could create a staircase and walk to the moon, would escape velocity still be a factor in leaving the Earth's gravitational pull? I'm not a physicist but am just curious to know.


texts: Do planets migrate suddenly or gradually?

texts:
Current models of the configurations of the planets conclude that Neptune once migrated outwards. AFAIK this refurbishment came about by Jupiter and Saturn gradually getting into and leaving a gravitational resonance.

Did Neptune (and possibly a fifth giant planet) redirect itself in a sudden encounter event, like comet 67P Churyumov–Gerasimenko did in 1959, halving the perihelion of its orbit since then? Or did it happen gradually over maybe millions of years? Is planetary migration in general sudden or gradual? Is it a matter of a single encounter event, or an adaptation to a changing gravity landscape?


texts: What is the minimum meteor size to see a falling star?

texts: When a meteor is going through our atmosphere you will see a light beam made by the gas the meteor compressed. But what is the minimum size to see a 'falling star'? Is a 1 mm3 meteor visible?


texts: How likely are planets to form after neutron star collisions?

texts:
It is well known that planetary collisions can create moons orbiting the result of the merger if they happen in the correct way, and this is how the Earth's moon is believed to have been formed. See the animations on this Durham University page to get an idea of how the mechanism works http://icc.dur.ac.uk/giant_impacts/.
It seems to me that it should be at least theoretically possible for the same process to happen when neutron stars collide, which would produce bizarre extremely-high-metallicity (or rather high-average-atomic-mass) planets. However, I also know that the physics is very different in some ways: the colliding objects are much denser; the collision is much higher-energy; radioactive decay creates a burst of extra energy from any matter thrown off the objects; the gravity and velocity are high enough that relativity matters a lot; they probably are in very circular orbits spiraling toward each other rather than hitting each other from the angles that protoplanets do; etc.
It's also possible that most of the mass of the neutron star might be thrown away and leave a low-mass remnant that might expand into an high-atomic-weight planet or white-dwarf, or that some bit of ejected matter might be thrown out at similar enough velocities (speed AND direction) to eventually coalesce into a rogue planet.
I'm just wondering whether anyone has looked into this before, or if anyone has any input as to whether this would be more or less likely than moons forming from planetary collisions, or if anyone knows how to test this with simulations.
EDIT: I've just realized the reason why it is probably impossible for a planet to form in the same way the Moon formed around the Earth: The outward force is way stronger than gravity except for close objects, which would be inside the Roche limit of the resultant black-hole or neutron-star and thus form an accretion disc or ring rather than a planet (due to the fact that any potential planet would be ripped apart by tidal forces). I haven't done any math on this, and this is just my impression, though. In addition, this doesn't mean a planet couldn't form from the ejecta in other ways; for instance, the disc of matter close enough to be held in orbit after the initial explosion might be pushed out to include a planet-forming region outside the Roche limit during a later phase of the event.
EDIT 2: I've had an idea for how this might happen, but I think this might really be a different question. The idea is that, if another star was in the same system as a kilonova (collision between stellar remnants that ejects matter and radiation), the kilonova might leave enough of the star to stay in the system, or perhaps leave enough matter for the other star to capture it somehow. One thing about this scenario, though, is that the idea of another star being in the same system as a compact binary merger rather implies that this third star has already been hit by at least one supernova, possibly multiple and maybe several novae, depending on whether a parasitic binary was formed. (This wouldn't apply if the third star was captured into the system after both of the other stars had already died, though.) Supernovae are stronger than kilonovae in terms of energy that gets thrown out, so the previous supernovae would already have had a stronger affect on the object. I believe that kilonovae are thought to produce heavier elements than any type of supernova, so stars hit by kilonovae would be different in composition than ones hit by supernovae, but it's still basically the same question: What kind of remnants can survive from stars hit by supernovae/kilonovae/novae at close range. I think it's pretty obvious that this could form some kind of remnant, possibly depending on the distance to the third star, so that already answers my question, though I don't know what compositions are possible or what masses are likely, but I think this is really a different question that should probably be asked separately if I or anyone else want it answered on Stack Exchange.


texts: How much light comes from quasars in an AGN?

texts: From what I've been able to gather, the very bright spot at the center of galaxies is produced by both the central quasar and a dense cluster of millions of stars that surround it. How much of the central light is produced by the quasar, and how much comes from the star cluster?


texts: Why is the universe full of spinning objects?

texts: Almost all celestial objects are rotating in some way about their axes. Why is this and should we expect the rotation to slow as the universe ages?


texts:
Galaxies stay at same place but it's the space that splits the galaxies apart. Is my understanding correct?

As per my understanding. Galaxies moving apart at high speed is due to the increase in space between the galaxies (i.e. new space is created between galaxies that push the galaxies apart). That's why it's said that every point in universe is center of the universe because after bigbang space has been created between galaxies and it started splitting the galaxies away.

Is my understanding correct?


texts:
Is there a place on Moon (sure it's near north or south pole) that is always lit by sun? It's to install solar panels if I will choose to make rancho there :)

What diameter of Moon Polar circle?
How high the hill or mast on the pole should be to be always lit?

I used some online calculators and found next:

  Axial tilt to ecliptic is 1.5424°, Lunar Radius 1738km

  Polar circle is 46.8km

  Spherical cap height 0.15km

Are my calculations correct? It shows that it should be near 150 meters high. Is any high enough hill exists on a poles?

P.S. Where I can check good 3d model of Moon with elevation (sure there is no sea level but ideal sphere)?

Thanks


texts: Will the 2016 Perseid meteor shower be visible in Sydney, Australia?

texts:
As the title states, will viewers in Sydney, Australia be able to see the Perseid meteor shower in August, 2016? Assume the viewer is well outside of the city and light pollution is a minimal problem.

According to Australian Geographic, the event will be visible in the northern parts of the country – specifically, "head north for the best chance to witness the event" – but it is not clear whether it will be possible to see anything in the southern parts.

If any viewing is possible, what would be the recommended dates and time of night to see the most?


texts: Does our sun/solar system orbit around any other celestial objects?

texts:
Does our solar system orbit around another massive celestial object? Like a massive star or black hole for instance? From my understanding our sun rotates around the centre of our galaxy, thus our solar system follows. But I'm curious to know if there is/are other(s) gravitational force(s) that affect our suns? Other than the rotation around the centre of the milky way.

It would make sense to me that the gravity of massive objects would affect our sun, which in turn would affect our solar system, but I cannot find any answers other than ones concerning the "galactic year".


texts: If Jupiter were to absorb all other planets in the solar system, would it reach degeneracy pressure?

texts:
Jupiter's mass is about the maximum a planet can be before it starts to fuse hydrogen in its core and undergo a massive transformation.

Total mass of all solar system objects in question is: here.

Jupiter is 1 Jupiter large, while the summation of all else is 0.405 Jupiter large.

Given the mass of Jupiter and the mass of all other planets, if Jupiter were to somehow collide and "absorb" all mass from every planet in the current solar system, would it turn into a star?

I guess that you can distill this question down to:

If Jupiter were 1.405x more massive, would it be a star?

Note: Still kind of new to these concepts, please explain misconceptions I may have.


texts: Could anything consume a small black hole?

texts:
Whenever I read about black holes, it is normally involving how they devour anything that comes too close... regardless of how big anything is.

But what if it were a really small black hole vs something really large? How about something like a large star or neutron star... could a black hole be small enough to get devoured / consumed by something like that or would it just not be possible?


texts: We seem to have named every moon orbiting other planets. Why haven't we named our own moon? And for that matter, why doesn't our sun have a name since we name or number stars?


texts: I am a high school student (going into 11th grade next year), who will be taking an introduction to astronomy and astrophysics as part of my core curriculum. As such, I would like to get a head start now, but I am not sure where to start.  Are there any specific learning resources that are recommended? Books, videos, documentaries?


texts: Is the measurement of distance and position of far away objects accurate?

texts:
Considering that light is affected by gravity, how accurate are our measurements of distant stars and galaxies?
When light passes through objects with great mass, such as Jupiter size planets, or black holes, shouldn't it change its course and result in a deviation of trajectory?
Does the light we see with telescopes when observing the many celestial bodies in the sky pinpoint the real location of such bodies in the past, or was its past location divergent from the point in space indicated by the light reaching us?


texts: Why not take a picture of a closer black hole?

texts: There are closer galaxies than Messier 87 for sure, even ours! It sparked my curiosity that they went with one 53 million light years away. Is there a reason for this?


texts: Sun constantly converts mass into energy, will this cause its gravity to decrease?

texts: If the sun is constantly converting the mass into energy, then will its gravitational field continue decreasing?


texts: Day/Night Cycles and Seasons if the Earth's Rotational Axis and Orbit Changed

texts:
I just enrolled in an introductory Astronomy course, and today in lecture the professor asked this question:

  Give 4 ways in which the day/night cycle and the seasons would behave on Earth if our rotational axis was in our orbital plane (Uranus is close to this). What about if the rotational axis was perpendicular to the orbital plane (so the ecliptic and Celestial Equator lay on top of each other), but the Earth's orbit was quite eccentric instead of almost circular?

For the first part, it means the Earth is rotating by North/South, right? Would this mean that the day/nights would be "flipped around," i.e. it would be night in a city when it would normally be day. I don't think the seasons would change, since the orbit remains the same.

I don't really know what the 2nd part is saying. Is it simply asking what would change if the orbit was eccentric rather than what it is now?

Any help or clarification on this would be greatly helpful. Thank you!


texts: With gravitational lensing, is it possible to mathematically compute the correct image of the galaxy that is being distorted?

texts: There's been another report of gravitational lensing in the news.  Wikipedia has a good image of an example of gravitational lensing taken by the Hubble Space Telescope.  This brings me to wonder that, since they understand the math behind the lensing, shouldn't they be able to reconstitute the original image of the galaxy behind the galaxy that is acting as a lens?  That is, take the image and run it through a computer program that reconstructs the image using known parameters of the mass and the position of the lensing galaxy?


texts:
NOAA GOES-14 & 15 went very recently in storage mode. With those also went the solar X-ray imagers (SXI), as GOES-16 & 17 do not have such instruments on board. Hence, my question:

Are there still any active solar X-ray imagers of other space agencies orbiting the Earth?


texts: Why do telescopes use hexagonal mirror pieces instead of pie slice shaped ones?

texts: Some new large telescopes in the near future, on Earth and in space, will use multiple mirrors. The individual mirror pieces will be hexagonal in shape. I wonder why this shape is prefered over the circle sector shape (like pie slices). I would think that corners and joints between mirrors cause practical problems. And a circle sector slice has half as many corners and two rather than three or six neighboring pieces, and shorter interfacing edges with neighboring pieces overall. So shy is the hexagonal shape prefered?


texts: How much magnetic attraction is there between the Sun and Earth?

texts: How much magnetism is there between the Earth and Sun? Would the distance from the Sun differ for not the Earth iron core and how much?


texts: Virial coefficient when computing dynamical mass enclosed by a rotating galactic disk of gas

texts:
Suppose I have a large thin disk of rotating gas in a galaxy -- the disk has a maximum inclination-corrected $V_{max}$ and a maximum radial extent of $R_{max}$ corresponding to that $V_{max}$ measurement. The virial theorem tells me that the total (aka dynamical) mass enclosed by that rotating disk (including stars, dark matter, etc.) is $V_{max}^2 R_{max} / G$, where $G$ is Newton's gravitational constant. Here I have assumed that the virial coefficient is 1, but the virial coefficient can vary widely based on the geometry of the problem. For example, it can be almost 10 for dwarf galaxies (an order of magnitude!), or a factor of $\sim3-5$ for dispersion-dominated rather than rotation-supported systems like elliptical galaxies where you're using the stars to probe the dynamical mass.

My question is simple: for a simple rotating disk of gas as above (assume it is thin and obviously not dispersion-supported, which I think is one of the simplest possible geometries for a question like this), what is the virial coefficient? I have seen coefficients of both 1 and 2, but I have no idea which derivation is correct. Adding to the problem is that some derivations seem to be using the virial theorem to give an order of magnitude estimate which means they leave out discussion of the virial coefficient altogether.


texts: How do we get radio signals of the big bang?

texts:
From TV shows I have known that we still get some radio signals of the big bang and they are every where. My question is is the universe expanding so fast that even electromagnetic wave has failed to cross it after big bang?

Or is it possible that there is another dimension that we don't know of? Like the earth is nearly flat and in small portion it's surface can be called 2d. But it possible to go "straight" and come back at the same spot as it is in "3d space". So is it possible that the space is 4d and somehow light has crossed the cosmos several times?


texts: What's the significance of finding neon on lunar atmospehere? new explanation of moon light?

texts: Now that NASA's LADEE spacecraft has confirmed the presence of Neon in the moon's atmosphere could the official explanation of the moon's light end up being change from reflecting the sun's light to some sort of electromagnetic interaction with the neon caused by solar winds, or something like that?


texts: How do we find the exact temperature of a star?

texts: This is a very basic question, but I am a little confused. As far as I know, the temperature of a star is analyzed based on the color of the light it emits. So, if a star is moving away from us, then the light emitted by it will be redshifted(or if it is stationary with respect to us and the light undergoes gravitational redshift), then how do we know the exact temperature of that star or any other object because it is possible that we observe red light but actually the star might be emitting yellow light.


texts: How did the reionization epoch make the universe "transparent"?

texts:
I've been reading about the reionization epoch of the universe, and it isn't entirely clear to me.

As I understand it, very shortly after the big bang the universe was ionized, with the electrons stripped from the protons of hydrogen. The way that it's described is that the universe was "opaque" (since it was filled with ionized gas). Then the universe cooled enough for neutral hydrogen to form again, and the universe became "transparent". When the first stars and galaxies began to form they reionized the universe.

What I don't understand is that in illustrations of this reionization, during the reionization epoch, it seems that the universe isn't transparent, but filled with unionized IGM (neutral hydrogen). Then the ionizing radiation from the newly formed stars ionizes the medium and ... these bubbles of ionized regions grow and merge until the entire universe is ionized again (and is therefore transparent).

Have I misunderstood when the universe is transparent? Or the definition of transparent? Would it be accurate to say that the present day universe is completely ionized? (Does this just mean that most matter is in the form of stars which can be considered ionized? Since it doesn't really seem immediately evident in everyday life that "everything is ionized")


texts: Minimum telescope needed to see the rings of the Saturn

texts:
I am a total novice. My daughter, likes Saturn.  Since Saturn is so close I thought it was a good time to view it with her.
What are the minimum needed telescope specs?
Update: Can answer answers be put in terms of magnification? Or the specs?


texts:
I'm working with some NEOWISE images that seem to have incomplete header tags. I've been advised by the SAO (because I'm using DS9 to view them) that I have

"a partial PC matrix defined, yet it does not conform to the FITS WCS standard. With a combo of CDELT and PC keywords, the CDELT keywords hold the scaling factor, the PC keywords, the rotation matrix, which should be normalized. If you want the rotation matrix to also contain the scale factor, use CD keywords".

Here's one of the headers I need to fix:

SIMPLE  =                    T / conforms to FITS standard
BITPIX  =                  -32 / array data type
NAXIS   =                    2 / number of array dimensions
NAXIS1  =                 1459
NAXIS2  =                  903
WCSAXES =                    2 / Number of coordinate axes
CRPIX1  =                729.5 / Reference pixel for axis 1
CRPIX2  =                451.5 / Reference pixel for axis 2
PC1_1   =     -0.0333333333333 / Coordinate transformation matrix element
PC2_2   =      0.0333333333333 / Coordinate transformation matrix element
CDELT1  =                   1. / [deg] Coordinate increment at reference point
CDELT2  =                   1. / [deg] Coordinate increment at reference point
CUNIT1  = 'deg     '           / Units of coordinate increment and value
CUNIT2  = 'deg     '           / Units of coordinate increment and value
CTYPE1  = 'GLON-AIT'           / Projection for axis1
CTYPE2  = 'GLAT-AIT'           / Projection for axis1
CRVAL1  =                   0. / [deg] Coordinate value at reference point
CRVAL2  =                   0. / [deg] Coordinate value at reference point
LONPOLE =                   0. / [deg] Native longitude of celestial pole
LATPOLE =                  90. / [deg] Native latitude of celestial pole
RADESYS = 'ICRS    '           / Equatorial coordinate system
BAND    = 'W1      '           / Wise Band
END

I've already managed to fix a couple of the invalid tags, but apart from these minor edits, this is unaltered from the file that my research supervisor gave me. The FITS standard here gives descriptions of each of the tags, but I'm not sure how to implement the SAO's advice. Can anyone help me fix the tags?


texts: Plotting Equatorial coordinates to X,Y plane (simulating telescope/camera view)

texts:
I would like to simulate a telescope camera view, projecting (RA, Dec) coordinate sets to a 2D plane. So effectively the need is to convert Equatorial coordinates to (x, y) coordinates, when we can know how many degrees a single pixel spans.
For convenience I'm using degrees for RA and Dec here, and the code is just pseudocode.
The following base information is provided as an example:
Imaging equipment:

Telescope focal length in mm (flen): 420
Image resolution (widthPx, heightPx): 4000 * 3000
Pixel size in microns (pxSize): 8
Binning (bin): 1

So from my understanding we can calculate a few things from this for starters.
The field of view in degrees should be:
fovW = radToDeg( 2 * atan((pxSize * bin * widthPx / 1000) / (2 * flen)) )
fovH = radToDeg( 2 * atan((pxSize * bin * heightPx / 1000) / (2 * flen)) )

And from this we could derive:
pixelsPerDegWidth = widthPx / fovW;
pixelsPerDegHeight = heightPx / fovH;

For locations closer to the equator I can get some valid looking results using this formula:
deltaRa = starRa - imageCenterRa
deltaRa = deltaRa > 180 ? 360 + deltaRa : deltaRa
deltaDec = -1 * (starDec - imageCenterDec)

posX = deltaRa * cosdeg(starDec) * pixelsPerDegWidth + 0.5 * widthPx
posY = deltaDec * pixelsPerDegHeight + 0.5 * heightPx

With some catalog star positions projected using this formula, I can even get Astrometry.net solver to correctly identify the center position.
However when we move to the poles this comes crashing down.
So let's go ahead and use a target center point near the pole:

RA 30 degrees (imageCenterRa)
Dec 89 degrees (imageCenterDec)

Let's also say that we have a hypothetical star at RA, Dec (220, 89.2) - this is close to the pole, and both the star and the pole gets included in the image.
What kind of formula should we use to get the correct location and to draw the area correctly even in the polar regions?
I've been looking for an example for a while but haven't come up with any. I've seen some formulas that may be just the thing I'm looking for but my thick skull loves examples - hence why I included some exact numbers here, as I would love to see how this would be calculated in practice.
So to summarize: how would we calculate the (X, Y) coordinate in the image for the star at RA, Dec (220, 89.2)?


texts: When did people first measure that the Earth was closest to the Sun during January?

texts:
When we talk about the reason for the seasons, we usually have to dispel the misconception that seasons are caused by being close and far away in the Earth's elliptical orbit.

And usually, we mention that the Earth is actually closest to the sun in January, in the dead of winter (for the Northern hemisphere).

But when did astronomers first have the Earth's orbit measured carefully enough that they knew the Earth was slightly closer during January?  How was that measurement made?  How accurate were the first measurements?

They didn't they measure the size of the disk of the sun very, very carefully, did they?  Perhaps with a pin-hole camera?  That seems like it would be very difficult to do.

Additional

I guess if we are talking about long enough ago, they would have thought it was the Sun's orbit that brought it closer because either because of an eccentric (the idea that the orbit of an ancient planet had a center that was offset) or because of epicycles bringing the Sun closer on the circle on a circle.

I just wonder what sort of observation they might have made.

One of the nicest comparisons I've seen can be found here.

If it was me with the tools available in ancient times, I'd probably use a rotatable camera obscura, and maybe a cone with markings to place at the center of the image of the sun, to exaggerate the effect of the size differences.

Second Additional

Based on JdeBP's answer I want to see if I have the correct concept.  (I would put this in comments, but comments can't be nicely formatted.)

Doing a search for the dates and times of the solstices and equinoxes, and finding the time between those dates and times, I found the lengths of the upcoming seasons.

Summer 2020 is 93 days, 15 hours, 47 minutes

Fall 2020 is 89 days, 23 hours, 0 minutes

Winter 2020 is 88 days, 21 hours, 7 minutes

Spring 2021 is 92 days, 17 hours, 54 minutes

Summer 2021 is 93 days, 15 hours, 49 minutes

If we subtract from 1/4 of an astronomical year, we get about:
$$
\begin{matrix}
Spring & +1.4 \: days & & Summer & +2.4 \: days \\
Fall & -1.4 \: days & & Winter & -2.4 \: days
\end{matrix}
$$
From there it seems like with a geocentric model with an eccentric, we could get a good approximation for the date of perihelion.

I'll have to think about the details of how to get there, though.


texts: Question about mass growth rate for individual planetesimals

texts:
In one stage of classic accretion, the mass growth rate with time (dm/dt) for individual planetesimals is proportional to $m^{2/3}$ and in another stage it is proportional to $m^{4/3}$.
My question is why are the exponents different? Which stage is a runaway and which stage comes first?


texts: Could a black hole pass quiescently through the Oort cloud?

texts:
Imagine a stellar-mass black hole passing through the Oort cloud, perhaps a quarter  to half a light-year from the Sun. How black would the black hole be? That is, any matter that fell into the black hole would release energy on the way in, and we know there are comets out there, and presumably smaller objects down to microscopic dust. But we also know they are very few and far between. Has anyone done a serious analysis of whether there would be enough infalling matter for the resulting radiation to be detectable?

As two commenters already recognized, this really is about radiation from infalling matter, and not the broader question of how we could detect such a black hole. Answers to that broader question in the comments are interesting, though.


texts: What are the Earth-like features of Titan?

texts:
This NASA site says that hidden beneath the smog of Titan are Cirrus like clouds and This space article describes how Titan's atmosphere is similar to Earth's too.

What other features does Titan boast that make scientists so ready to boast that "Titan may well be the most Earth like planet we know of besides Earth itself"? (paraphrased)

Answers should focus on the features of Titan itself, obviously a similarity is that it orbits the same Sun, but this type of thing is not what I'm after. I am mainly searching for geological or atmospheric similarities that Titan shares all the way down to potential similarities in the composition and flow of the planetary core.


texts: I recently upgraded from a Meade ETX-RA to and ETX-EC and bought a used Audiostar controller. My EC came with a Meade autofocuser and one of the old (I think it’s 494) controllers that has the focus controls and the four lights on it. Is it possible to just plug the autofocuser AUX cord into the Audiostar and focus from that? I read the manual for the autofocuser and it seems like I should be able to. Just not sure which controls I am supposed to use.


texts: Given a date obtain latitude and longitude where is the sun zenith

texts:
Searching is easy to find terminator line (frontier between day and night) or the position of the sun in the sky given a position on the earth and a time; but I can't find how to obtain where is the zenith of the sun given a date (and time).

I need to obtain the center of the illuminated zone of the earth (latitude and longitude) at a given time. (Well, actually I need the opposite, the Nadir, but with one you can calculate easily the other).

Any knows the function?

Thank you.


texts: Calculate NEO object position with nasa Near Earth Object data

texts:
I wish to create a 3D visualisation of NEO's by date in relation to earth, but calculating their position at that time has got me stuck.

From this question I was able to fine Nasa's NEO object data:

Previous Question

Listing Of NEO's:

Nasa Date range NEO Data

Detailed NEO Data

Given the information in these JSON streams. Is it possible to calculate the position of the NEO in relation to earth? It doesn't seem to offer any positional information that I can see, although this is not my field.

Or is there a better data set which will assist me in this?


texts: Is there any average value for the Alfven radius of main-sequence stars? if there are no such values, then how may I calculate it??


texts: Is it possible to affect Earth's orbit so that, say, aphelion happens sooner?

texts:
As part of its natural cycle, the sun is currently drifting away from the Earth, it's predicted to reach its farthest point by July 4th in 2020, at which point the distance between the Sun and Earth will start to close.

Do humans have enough power to control earth's orbit so that the sun starts its trip back sooner? I just can't wait for the heat to come back.


texts: Do Roche limits apply to Kerr ring black holes?

texts: I was wondering if a smaller black hole orbiting a larger one  could be torn apart by the Roche limit or tidal force or other, if the center of the blackhole was not a singularity but a Kerr ring of Neutrons?


texts: Why is the Cosmic Microwave Background at the same distance no matter the direction we look?

texts:
I've read from different sources that:

The CMB is visible at a distance of 13.8 billion light years in all
directions from Earth, leading scientists to determine that this is
the true age of the Universe.

And that got me thinking, if this is true, there are 2 possible scenarios:

These are not really the true limits of the universe, but it's the farthest we can watch with our actual technology.
Or we happen to be the center of the universe, because we see the "beginning" of it at the same distance no matter the direction we see at (which I think this a dumb supposition)

So, why do we actually see the CMB at the same distance no matter what direction we look at?


texts: Are there any estimates for the combined mass of all near earth objects (NEOs)?

texts:
I tried looking around but couldn't find any sources attempting to answer this particular question.  It's obviously impossible to know the exact answer, but all I'm looking for is an estimate.  My best guess would be that it's about a tenth (or less) of the mass of the asteroid belt, with a composition roughly 10-15% metallic and 85-90% carbonaceous or silicate.  Is anyone aware of any sources that attempt to give an estimate?  If not, what would you say is a reasonable estimate?

Thanks in advance.


texts:
In the popular TV show The Big Bang Theory Season 3, Episode 4, Sheldon Cooper said that astro means star and Raj said astro means space, I got a little confused here, various websites and others are going 50-50 on the subject. What does astro actually means?

Raj: No, no, no, no! That rate is much too low for what we’d expect from this collision. Do you understand that we’re talking about dark matter colliding in outer space?
Sheldon: Of course I understand. And who are you to tell me about outer space?
Raj: I’m the astrophysicist. Astro means space.
Sheldon: Astro means star.


texts: Composition and Proton Flux from the Solar Wind

texts:
I am taking a class on the space environment and I have a few questions about the solar wind.  A number of sources list the composition as (approximately) 4% He$^{++}$ and 96% H$^{+}$.  What exactly does this mean?  Does it mean by mass or by number of ions?

Also, when discussing proton flux due to the solar wind at Earth:  What exactly is included in the flux numbers quoted (e.g., one source I have says 2e12 m$^{-2}$s$^{-1}$).  Is that the flux due to only the H$^{+}$ and excluding the He$^{++}$ and other minor constituents?  Or, are they including all the protons from the other ions as well?


texts:
I have a simple question which I think about often but have no answer.

If The Big Bang is true, than if the whole space was just a point 14 billion years ago, then what was around that point, some other kind of "space" or nothing? In latter case how do we define nothing.


texts:
Assume two black holes collide head-on.  In other words, they were not orbiting one another before the collision.  I know this is unlikely.  Further assume that their sizes and distance from Earth are similar to past collisions detected by LIGO.

My understanding is that detectable gravitational waves are caused by massive objects undergoing massive accelerations and that detections so far have been of colliding objects orbiting one another many times within a fraction of a second.

I assume that a head-on collision would create a single gravitational "pulse" instead of a wave.  I don't know if "pulse" is the right word for this.  Would this pulse be detectable by LIGO?


texts: Do the terrestrial planets form later than gas giants in our solar system?

texts: Sorry I forgot where this statements come from, but I also remember the reason behind it is due to young Jupiter moves inwards and destroys the original super earth in inner solar system, and the current terrestrial planets are formed after that, is that true?


texts:
Where can a gallery of actual unaltered photographic images taken in (or of) space be found? Specifically ones that are untouched, not colorized (not necessarily black and white, but they usually are), and taken by natural light photography? Pictures and videos claiming "actual image" are few and far between.

E.g., this:

Not false color:

Both of these pictures are from NASA's (Voyager) Saturn Images gallery. Some of the other ones there are listed as false color, some aren't (but obviously they are). Or maybe not so obviously, hence the question: what does it really look like out there?

I've a pretty good idea of what Saturn looks like IRL, because I've seen it in a telescope (exactly like the first picture, except it's more colorful - absolutely nothing like the second). For most other celestial objects, I have no such baseline.

The title of the website I'm looking for would be along the lines of: View of our solar system through the eyes of a human. Decidedly, not containing any pictures from the HST, as all of them are photoshopped.


texts:
The question Who was the first to realize that the Earth is surrounded by vacuum? was closed because some users felt it was answered by answers to a different question in an different SE site: Who was the first to postulate that space was a vacuum?

To me the distance between realize and postulate is astronomical!

That aside, I've asked a new question: What was the first astronomical measurement which demonstrated that "the Earth is surrounded by vacuum"?

By demonstrated I'm talking about a measurement that shows it is, or at least is likely to be the case that Earth is surrounded by vacuum. It should be something such that it could be presented as scientifically convincing evidence to other scientists of the time, unencumbered by non-scientific predispositions (e.g. religion, rivalry, philosophy...)


texts: Assumptions necessary for the strong form of Olber's Paradox

texts:
From Wikipedia, here's Lord Kelvin's statement of Olbers' Paradox:

  Were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the Galaxy – since there could be absolutely no point, in all that background, at which would not exist a star.

This is one form of Olbers' Paradox I've heard, which is that with infinitely many stars scattered in an infinite volume, every ray must eventually intersect a star. I call this the "strong form" because it seems to me stronger than the statement that infinite stars imply an infinite amount of light hitting every point, though not necessarily from every possible direction.

The strong form of the paradox doesn't hold if each star is a point mass and there are countably many stars, since the number of rays from any given point is uncountably infinite. Or imagine instead that stars are balls with small positive radius. If there is such a star at every lattice point in $R^3$ (an assumption that is consistent with my crude understanding of the cosmological principle), I can easily find a ray that intersects no star. I start from (0, 0, 0.5) and choose the ray in the direction of (1, 0, 0.5); the z coordinate will always be 0.5 and therefore my ray will never come close to a lattice point.

Is there another, palatable assumption we can add to make the strong form of Olbers' Paradox true, perhaps an argument that the distribution of stars must be more random than what I've described?


texts: does the orientation of orbital plane of our solar system rotate with the galaxy

texts:
As I understand it, our solar system travels through the milky way with the orbital plane tilted about 60 degrees so that we are sort of traveling in the direction of earth's north. My question is if our orbital plane rotates with our galactic orbit so that it maintains its orientation in relation to the center of the galaxy as I've show in this first picture.

Or is the orientation unaffected by the galactic orbit as I've shown in this second picture.


texts:
I'm looking for the parameters $r_c$, $\rho_0$ and $\beta$ in a $\beta$-profile fit of the Virgo cluster's ICM density. I just can't find a reference for it. Unlike for Coma (Abell 1656) where it's in Mohr et. al. 1999.

Beta profile:

$$\rho(r) = \rho_0 \left[ 1+ \left(\frac{r}{r_c}\right)^2 \right]^{-\frac{3\beta}{2}}$$


texts:
Probably a stupid question, but it "bothers" me and I can't find a concrete answer on the internets.

When you fall into a black hole, afaik, time slows down for the matter falling in as it gets blasted by high energy light incoming as the universe speeds up, relative to that matter.

Doesn't that mean though that the matter falling in never completely reaches the center?

It seems that the "core" of the black hole would be made of whatever was there at the time of the collapse with time not really flowing for it, and incoming matter would slow down as it fall and be in a almost suspended state as it gets closer to center through the event horizon.

But again, all my knowledge here is based on random YouTube, so I'd love to learn more about it if there are any resources touching that aspect...

Thanks!


texts: How are comet and meteors made, and what causes them to travel through space so fast? I have tried researching, but I decided this was the faster way.


texts: Is Earth's orbital eccentricity enough to cause even minor seasons, without axial tilt?

texts:
I was reading the answers to this question about an exoplanet having seasons without axial tilt, and several responders mention that orbital eccentricity could cause a similar effect, but that the orbit would need to be "very eccentric," as opposed to Earth's, which is "very close to circular."

If the Earth had no axial tilt at all, would its eccentricity be high enough to have any discernible effect for the inhabitants?  Even if it didn't cause major shifts in temperature, would it be enough for pre-scientific people to track the passing of years?


texts: Has stellar evolution ever been modeled analytically?

texts:
I'll still remember the handout my astronomy professor gave us more than several decades ago; Our Friends the Polytropes. We spent a lot of time learning how polytropes, simple analytical power-law models could reproduce some basic thermodynamic properties of stars, and how those properties would tend to vary with mass (and perhaps other parameters, I don't remember now).

Have polytrope models of stars (or other simple analytical models of stars) ever been "evolved" analytically in time? In other words, in addition to variations on radius, have a set of equations ever been written which also included a $\frac{\partial}{\partial t}$ in such a way that they were amenable to an analytic solution?

note: I've added the history tag since I'm asking about the "gold 'ole days" rather than about modern techniques.


texts: If a planet gained too many moons could the tidal forces of those moons rip the planet apart?

texts: Or would the planet just be subject to extremely intense tidal forces instead?


texts: How long do other planets in our solar system have total solar eclipses?

texts:
Jupiter, Saturn, Uranus and Neptune — can all have total solar eclipses so how long do they last?
https://www.livescience.com/amp/60037-do-other-planets-have-solar-eclipses.html


texts: How do radio telescopes gather information about visible light?

texts: Is the first image of a black hole that was captured by the Event Horizon Telescope what would be seen with a large enough optical telescope (or with the naked eye from a proper distance of the black hole)? If so, how do radio telescopes gather information about visible light?


texts: What are some night sky objects I could see with my Celestron UpClose 20x50 Porro Binocular?

texts:
I bought this binocular because I've read countless times that one should start with a pair of binoculars before diving into telescopes. I've seen details of the moon and I can notice Venus round shape on some nights. I also saw Jupiter and it's two larger moons, as faint as the faintest stars, but this was on a beach trip so the sky was clearer than what I'm used to.

I live on a place with a 7 or 6 on the Bortle Scale, is there something else I should try to see?


texts: Planetary system orientation & the search for exoplanets

texts:
A quick review of photographs of galaxies will reveal that not all galaxies are orientated in the same plane as the field of view from Earth. Some galaxies are parallel to our field of view and we see them side on. Others are perpendicular to our field of view and we see them as if we are looking either from above or below them.
Given this fact, it would be fair to assume that the orientation of planetary systems is similarly varied. Not all of them are parallel to our field of view.
All the exo-planetary systems I am aware of have been seen in a side view perspective  and any exoplanets have been detected by either a wobble of the star at the center of the planetary system or via dimming of the star's light as the exoplanet transits the star.
Have any exo-planetary systems been discovered that are perpendicular to our field view, looking from above or below the system and if so, how have any exoplanets in these systems been detected? If no such systems have been observed, how would astronomers detect exoplanets in such systems?


texts: How did they measure the distance to the center of our galaxy to 0.3% accuracy?

texts:
The abstract of A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty (Open Access) says:

  We present a 0.16% precise and 0.27% accurate determination of R₀, the distance to the Galactic center. Our measurement uses the star S2 on its 16-year orbit around the massive black hole Sgr A* that we followed astrometrically and spectroscopically for 27 years. Since 2017, we added near-infrared interferometry with the VLTI beam combiner GRAVITY, yielding a direct measurement of the separation vector between S2 and Sgr A* with an accuracy as good as 20 μas in the best cases. S2 passed the pericenter of its highly eccentric orbit in May 2018, and we followed the passage with dense sampling throughout the year. Together with our spectroscopy, in the best cases with an error of 7 km s−1, this yields a geometric distance estimate of R₀ = 8178 ± 13stat. ± 22sys. pc. This work updates our previous publication, in which we reported the first detection of the gravitational redshift in the S2 data. The redshift term is now detected with a significance level of 20σ with fredshift = 1.04 ± 0.05.

and figure 2 shown below provides an example of the error analysis post fitting.

If you have the angular size of an orbit and a set of radial velocity measurements, even if it was viewed edge-on and the inclination was known, wouldn't this give only a parametric relationship between R₀ and the mass of the central object?

I don't understand how they were able to state a specific value for R₀, I'm probably missing something obvious but I can't figure it out. According to this answer:

  We have reasonably good measurements of the mass of Sagittarius A*, thanks to measurements of the movements of stars like S0-2 over several decades. It's been well-established that the mass of the central object is $M\approx4\times10^6M_{\odot}$;

so to me the whole situation appears on the surface to be circular referencing. I'm sure it isn't of course, I'm just missing something.
Is the measurement really to the "Galactic center" as the first sentence of the abstract states, or really the distance to Sgr A* around which S2 orbits?
"bonus points" Why is every instance of "Galactic" in this published paper (not a preprint) capitalized?

  Selected posterior densities as obtained from the MCMC sampler with N = 200 000, here for the noise model data set. The contour lines mark the 1, 2, and 3σ levels. We only show the diagrams with the strongest correlations. All parameters are well determined (see Appendix D). Source


texts: In a binary star system, what relation determines the eccentricity of the three orbits (for $m_1$, $m_2$, and the reduced mass)?

texts:
In a binary star system, why does $$e_1 = e_2 = e$$

where $e_1$,$e_2$, and $e$ are the eccentricities of the three orbits of $m_1$,$m_2$, and the reduced mass, respectively.


texts: Why is the statement "black holes make up 1% of the mass of the Milky Way Galaxy" unknown?

texts:
a) We cannot detect all black holes and therefore don't know the percentage of the galaxy's mass they make up.

b) We do not know the mass of the Milky Way's central black hole.

c) According to our understanding of stellar evolution, black holes should make up a much lower percentage of the galaxy's mass.

d)According to our understanding of stellar evolution, black holes should make up a much higher percentage of the galaxy's mass.

In my own understanding, I feel like it should be a). Since the black holes are forming all the time, I think it is hard to detect all of them. But I am not quite sure, could someone give any insight?


texts: What would cause large jumps in brightness during a solar eclipse?

texts: This question on Physics SE about apparent brightness during a solar eclipse has a log-scale graph of light intensity versus time.  Parts of it are the shape I'd expect: a nearly-smooth curve going from "extremely bright" to "very dim".  However, there's a great deal of apparent noise in the graph, with jumps of nearly a full division in the graph (corresponding to about a two-fold or eight-fold change in brightness, depending on if it's a natural or base-10 log).  What causes these jumps?


texts: Are there any star system(planet system) where a star revolves around a star? Is it theoretically possible?


texts: Looking for a Dwarf Galaxy < 500 L.y. in Diameter, which is not a Satellite / Companion, or is at least 500 000 L.y. away from another Galaxy

texts:
My goal is to learn about an example of a Dwarf Spheroidal or a Dwarf Irregular Galaxy which is not a Satellite / Companion Galaxy (or is at least 500 000 L.y. away from another Galaxy), and doesn't measure more than 500 Light years in Diameter.

I must say that merely learning whether such Galaxies exist or not, would also be extremely helpful.

Another great alternative would be a Galaxy of any shape as long as it's less than 500 L.y. in Diameter and at least 500 000 L.y. away from another Galaxy.

The perfect example however would be a Dwarf Spheroidal or a Dwarf Irregular below 500 L.y. in Diameter, at about the average distance away from another Galaxy.

I found a few lists of Dwarf Galaxies, but they are lacking details regarding the sizes.

Any help would be greatly appreciated. Thank you.


texts: There are many more stars in the universe than the years that the universe has been in existence, so wouldn't this mean that stars were/are forming at an astounding rate?


texts: Lights moving fast and in a straight line coming from the northwest headed southeast tonight at 9:15CST

texts:
What is going on tonight?
Bright lights in the same high orbit moving very fast across the night sky from Northwest heading southeast...then 10 minutes later same line but far fewer almost in identical location....this was at 9:15 CST tonight 4/26/20


texts: When a fast-moving star goes supernova, how will the resulting remnant evolve?

texts:
Let's take a massive star that has zero velocity. When this star goes supernova, the resulting supernova remnant will expand in a sphere. But, let's take a runaway star travelling at 200 km/s. I am predicting that the remnant will form a teardrop shape, with the rounded edge compressed a little with the rear end elongated.
My reasoning is that the material ejected "forwards" relative to the star's velocity vector will gain some velocity, leaving the dead star behind. However, the material ejected backward will lose velocity, meaning that it will stream out over a longer distance. So to a viewer it would look like a "cosmic fireball" in some sense.
Is this correct, and would there be anything that could change this result? If I am wrong, what would be the actual way that the remnant would expand?


texts: What is the naming convention for craters on Mercury?

texts:
The two largest craters on Mercury are names Caloris (meaning "hot") and Rembrandt (for the painter). So there doesn't seem to be a pattern.
By convention, craters on Mars are named for people who studied the planet (like Cassini) or wrote about it (like Bradbury).
Is there a similar naming convention for the craters at the surface of Mercury?


texts: About bias in sidereal time (used by astronomers)

texts:
I came up on this stanza in various websites when looking up on experimenter bias. It says

"If the signal being measured is actually smaller than the rounding error and the data are over-averaged, a positive result for the measurement can be found in the data where none exists (i.e. a more precise experimental apparatus would conclusively show no such signal). If an experiment is searching for a sidereal variation of some measurement, and if the measurement is rounded-off by a human who knows the sidereal time of the measurement, and if hundreds of measurements are averaged to extract a "signal" which is smaller than the apparatus' actual resolution, then it should be clear that this "signal" can come from the non-random round-off, and not from the apparatus itself. In such cases a single-blind experimental protocol is required; if the human observer does not know the sidereal time of the measurements, then even though the round-off is non-random it cannot introduce a spurious sidereal variation."

I understand that sidereal time is something related to the time measurement used by astronomers as a time-keeping system, but I don't understand by "someone who knows the sidereal time of measurement" can then unconsciously influence the results, because say if you saw the clock as 00.56 s and you rounded it to 00.6s, I don't think it will have any effect. But moreover, by rounding that, how can you tell it will eventually have effect on your results?

Please advise.

Sorry for any wrong tags. I'm new here, so still learning.


texts: Could a pulsar in orbit around a black hole feed the black hole with its radiation?

texts: Could the black hole consume the radiation? If so, could the pulsar radiation absorbed by the black hole make it grow steadily more massive over the course of billions or trillions of years?


texts: Why was this asteroid (4864 Nimoy) chosen to be named after Leonard Nimoy?

texts: The asteroid 4864 Nimoy was recently named after Leonard Nimoy. It was discovered on September 2, 1988 so it went nearly 27 years without a name. Why was this asteroid chosen to be named after him? Were they trying to think of a name for it and chose to name it for Leonard Nimoy, or were they looking for an asteroid to name after him and chose that one?


texts: How come, in our lifetime, we will see the first stars which ever formed?

texts: Isn't it an unlikely coincidence that we live in such special times, that we will have observatories (JWST) that see all the way back to the first starlight in the universe? Are we dreaming, and is it possible that we will be surprised and keep finding evolved galaxies more than 13.8 billion years old?


texts: What is the farthest object we've been able to bounce signals off of to date?

texts:
I know people bounced lasers off of Venus and Mercury in 1960s in order to test the Shapiro delay. Since then, we've developed higher power lasers and radio transmitters (Bolshakovo transmitter).

Are there any farther objects where we've been able to detect the reflected wave?


texts: Theoretical limits for natural satellites having natural satellites

texts:
Is there an inherent instability or limit that prevents natural satellites like the moons of Jupiter from having their own natural satellites?

I looked at other questions such as do moons have moons but they focus on discovery rather than theoretical limits analogous to the Roche limit for satellite formation.


texts:
Magnetars are the most magnetic things in our universe. Because of how powerful their magnetic fields are, they could split every single atom apart from each other in our body.

Because of this could they destroy planets (rocky or not)? If so, how close would the planet have to be?


texts: Why does gas form a star instead of a black hole?

texts:
When a space gas gets pulled together a star is formed. On the other hand, when a massive star dies, it collapses to a black hole.

You would think that the initial mass of the gas would be bigger than the star that had existed for billion years and lost mass in the process.

So what stopped the space gas from forming a black hole in the first place?


texts: Are red moons possible without eclipses or smoke from fires?

texts: This morning I was on the bus and as I looked out of the window I saw that the moon was larger than usual and red. I live in eastern Norway and it was about -20ºF / 30ºC outside. There's no forest fires, and I live in a small village. There's no eclipse scheduled either. The moon went behind the mountain line before I got to school ( bus ride happened  7:03 - 7:20 ), and nobody there had seen it. Can you explain this?


texts: Visible Light Ground-Based Solar Observatory Data Archives?

texts:
I'm mainly searching for the best(or good/significant/important) solar data archives via ground-based telescopes. If I'm not being very straightforward...

Say if I wanted high quality/resolution images of the sun, I'd use SDO/SOHO's data archives-- they're easily accessible, queryable, and yield impressive images. So I'm looking for mainly visible spectrum images from ground-based telescopes rather than space observatories, although differing spectral images will be used just less-extensively. I've struggled to find any good data archives, however. NSO's archives seem all over the place, although the data it yields is impressive; so, if you are knowledgeable on how to recurringly access and reconstruct their data, I'd be much appreciative. Otherwise, is there any other ground-based observatories' archives that are freely available to the public, easily accessible, and present data online that anyone has used or know's about? Jpeg, png, etc. are all valuable, but if you know of any that use different file formats, they'd also be greatly appreciated.

Keep in mind, I'm not looking to discuss/argue what the BEST one is, but rather what commonly used/good ones are. So, any and all input will be greatly appreciated, as my project is best researched with many differing observatories.

Lastly, the better the telescope's quality in which the data is made available through, the better. So McMath-Pierce and other impressive unit's data should and will be given precedence over telescopes of less accuracy.


texts:
I understand that the Universe could be either finite or infinite and that it is, at the least, "very large". :)

My question is, why doesn't the math involved in making the CMB and other predictions, in effect, tell us the size of the Universe? We know how hot it was then and how cool it is now. Does scale not affect these calculations?

In other words if a given volume is a million degrees on "day" one and it's now 2.5 degrees don't those temperatures change if you make the volume 200 times larger?

The calculations make the Observable Universe, the CMB and the temperatures then and now all come out right and validate the Big Bang theory. How can they do that with both a smaller Universe (Observable Universe) and the much larger actual Universe?

Is it just because whatever the size of the Universe is, it was all 1 million degrees (example) at one point? Otherwise, it seems the predictive math involved would produce different numbers for different volume.


texts: Explaining Dark Matter and Dark Energy to layman

texts:
With my little knowledge, I know this:

Dark Matter

The center of a galaxy controls/attracts its objects (stars, planets, comets etc.) towards itself because of gravity. But the mass of the center of this galaxy appears to be less than what it should take to attract all objects of the galaxy. Hence Dark Matter is there, which makes this attraction or controlling possible.

Dark Energy

This is the force which is pulling galaxies away from each other, and hence making the universe expand. If we don't have this hypothetical force, we cannot explain why distances between galaxies are increasing.

Question

Please let me know how far I am from the actual meaning/definition of these terms? And how can I explain these to a layman, who has no or very little knowledge about astronomy?

Thanks.

P.S.: I have read this question here, which is excellent but I could not get an idea of how to explain to a layman.


texts: In terms of power delivered to Earth, what is the brightest object in the sky?

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I was reading about TXS 0506+056, a distant blazar. The Wikipedia article mentions it is one of the brightest objects in the sky at both gamma and radio frequencies. This got me wondering — if we consider brightness in terms of total energy delivered to Earth, which astronomical object is the brightest?
I can find vague-ish almost-answers to this, but only for specific frequency ranges (e.g. Object X is rather bright at Y MHz, but incredibly dim anywhere else, etc.) and only for photons. I am interested in any mechanism of energy delivery (cosmic rays, photons, gravitational waves, etc.); although, I would imagine photons probably account for the majority.
Let us also say that the energy doesn't have to be absorbed, so that forms of energy to which the Earth is more-or-less transparent (e.g. neutrinos) are okay too.
You can define "source object" however you wish. Transient events are okay too. If you want to give numbers, flux densities at Earth or a total power integrated over its cross-section would be welcome.
The obvious answer here in the Sun, so we shall exclude it. I suspect that the Moon and maybe some planets will also be contenders, so let’s just constrain ourselves to extrasolar sources. Consider this the only constraint on candidates.


texts: What is length of the universe on lights perspective

texts: According to Einsteins theory of special relativity, when something is travelling close to light speed, travel path is contracted. When the traveller is light itself, does it see the travel path contracted to zero? In another word, does light see length of the whole universe is zero across its travel path? How?


texts: Why do pictures of the Milky Way look like a spiral?

texts: When I see pictures of the Milky Way they show a spiral shape. Why is this?


texts: Why does the 70-solar-mass black hole in the LB-1 system challenge current astrophysics?

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Recently scientists discovered a large stellar-mass black hole, which (previously) they believed that it shouldn't be possible in our galaxy!

Source

  An international team of scientists say they have discovered a
  stellar-mass black hole with a mass 70 times greater than the sun — so
  large it defies current theories on how black holes of its kind form.

Why shouldn't it be present in our galaxy system? Are there any physical or mathematical calculations that defy its existence?

References:

Chinese Academy of Sciences Headquarters Press Release
Nature Paper - A wide star–black-hole binary system from radial-velocity measurements
Nature EPDF - A wide star–black-hole binary system from radial-velocity measurements


texts: I need some help obtaining IR background diffuse data from the WISE observation. There is already some work done in this regard; see: http://wise.skymaps.info/ . These are .fits files. How do I find out the photon irradiance for a range (say glat b/w 0 and 30) from these files? Any help is appreciated. Also, how do I correlate this with UV flux for the same range using python?


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My scope simulator is pointing to the celestial north pole.
My position is 41º 27' lat and 2º 15' long.
At 12h 43m local time (11h 43m UTC) the coordinates read from the scope are:
RA: 16h 14m 25s
DE: 90º 00'00"
There seems to be a constant 4h 31m difference between North pole RA and UTC time.
What the relation is between UTC, my location and celestial North Pole Right Ascension ?
I am making all kind of operations trying to relate these numbers to no avail.
Sorry if it's too stupid a question. I try to create a model in my brain of how celestial movements work and at the moment I only manage to explode a few neurons. Getting a clear answer will help me get the puzzle together


texts: Why is the ring of light around the M87 black hole bigger than the photon sphere?

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Today we know that a black hole represents a region of space where the gravitational forces are very intense, this consequence of a concentration of matter in a very small region of space. On April 10 of this year, scientists from the EHT project (event Horizont Telescope) presented to the world the image that I believe everyone has seen. The first image of a black hole in the galaxy M87. We know that what we are really seeing is the "shadow" of the black hole.

But the "photon sphere", where light can orbit a black hole, is actually at $1.5R_s$, (Schwarzschild radius), whereas the observed ring is a factor of 2 wider than this. Why we not see a ring of light at the radius of the photon sphere?


texts: Is the Drake Equation an accurate way of finding the probability of life on planets?

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I was interested in finding out if there was life on any planets or moons. I saw ReNiSh A R's question, and I saw the answer about there being life on Europa, but it didn't accurately answer what I wanted to find out.

The Drake Equation is on: http://en.wikipedia.org/wiki/Drake_equation.

I have also heard that there could possibly be life in the upper atmosphere of Jupiter, which could have floating beasts, and also on Titan, which does have surface liquids, but I am pretty sure most of it is in solid form.

If the Drake Equation is equal to a low number, then why is it pretty common if there is a possibility of life on 2 moons and 1 planet? Does that make the Drake Equation a non-reliable source?

I'm also looking for an accurate answer, so can you please give it to me in detail!


texts: Is the point of this paper to say that Pluto's status as a planet should have been handled scientifically, rather than by a vote?

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The abstract of a paper currently in-press in Icarus: The Reclassification of Asteroids from Planets to Non-Planets (Metzger et al. 2018, https://doi.org/10.1016/j.icarus.2018.08.026) says:

It is often claimed that asteroids‘ sharing of orbits is the reason they were re-classified from planets to non-planets. A critical review of the literature from the 19th Century to the present shows this is factually incorrect. The literature shows the term asteroid was broadly recognized as a subset of planet for 150 years. On-going discovery of asteroids resulted in a de facto stretching of the concept of planet to include the ever-smaller bodies. Scientists found utility in this taxonomic identification as it provided categories needed to argue for the leading hypothesis of planet formation, Laplace‘s nebular hypothesis. In the 1950s, developments in planet formation theory found it no longer useful to maintain taxonomic identification between asteroids and planets, Ceres being the primary exception. At approximately the same time, there was a flood of publications on the geophysical nature of asteroids showing them to be geophysically different than the large planets. This is when the terminology in asteroid publications calling them planets abruptly plunged from a high level of usage where it had hovered during the period 1801 – 1957 to a low level that held constant thereafter. This marks the point where the community effectively formed consensus that asteroids should be taxonomically distinct from planets. The evidence demonstrates this consensus formed on the basis of geophysical differences between asteroids and planets, not the sharing of orbits. We suggest attempts to build consensus around planetary taxonomy not rely on the non-scientific process of voting, but rather through precedent set in scientific literature and discourse, by which perspectives evolve with additional observations and information, just as they did in the case of asteroids. (emphasis added)

On the website there is also:

Highlights

The literature on asteroid classification is reviewed from 1801 to the present.
Scientists considered asteroids to be planets until the 1950s.
Thousands of asteroids sharing orbits was not debarring from planet status.
They were reclassified as non-planets on the basis of geophysical characteristics.
Taxonomical terms like planet are determined by the scientific process, not voting. (emphasis added)

It sounds like they are saying that Pluto's status as a planet was removed by a vote, more than by scientific consensus, and that while the title suggests that the paper is about "Asteroids" it seems the scenario might actually be proxy for Pluto's demotion.
Question: Am I misunderstanding, or is that really the main point of the last few sentences of the abstract, if not the entire paper?
Here's an example of another situation of classification being in flux: Do astronomers generally agree that the distinction between comets and astroids is not so clear?


texts: Is it safer to be near a star or a black hole?

texts: If a star or black hole neared the solar system, which would do the least damage?  For the sake of a good comparison, lets assume the candidate star is an "average" 5 solar mass star, and the black hole is a 5 solar mass black hole.  My thoughts at first were that the star would be the least devastating, but now that I think about it more, since not even radiation, etc... is being emitted by the black hole, (except possibly from hawking radiation and from any in falling matter), the black hole might actually be safer!


texts: Do astronomers generally agree that the distinction between comets and asteroids is not so clear?

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edit: I just saw this tweet and find it incredibly relevant :)

begin question: See this answer and then consider if there are known or likely solar system bodies that might be identified as both asteroids and comets.
If so (there seems to be an example there) would this be because there is insufficient information known about the body, and the ambiguity could be cleared up with enough data (say a visit by a spacecraft)?  Or are the categories of asteroids and comets actually overlapping?
If the latter, is there work underway to improve or update these definitions?


texts: Question about redshift and effective gravity at the rotating neutron star surface

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For a rapidly rotating neutron star, if consider the star as a sphere, redshift at the equator surface will be larger than at the pole. But if consider the star as an obsolate sphereiod (the ellipsoid varies according to the rotation velocity), then how about the redshift at equator compare to the pole surface? Whether the obsolate decrease the redshift at equator?
Similar is the effective gravity, if consider the obsolate effect, how about the gravity difference between the equator and the pole compare to that a sphere?


texts: Why is the Earth's magnetic field stronger than its neighbors?

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[Edited] I've learned that the Earth's core is hot due to decay of radioactive elements, causing the liquid part of the core to stay liquid. This was stated as an explanation to why the Earth has a strong magnetic field.

Assuming the rocky planets were formed roughly the same way (planetoid collisions etc.), why was Earth the "lucky winner" of abundant radioactive elements, while Mars & Venus were left with much less, causing their cores to solidify, their magnetic fields to weaken, their water blown into space, and their fate sealed to become arid desert and boiling inferno, respectively?


texts: Amateur observing targets for binary star systems?

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Are there any easily resolvable, binary star, observing targets visible from ~N40°?

I'd like to be able to show, in one observing session, Mizar and Alcor (naked eye resolvable), another with binoculars, and finally one in a small (say, 4 to 6" reflector) amateur scope.


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What is/was the motivation behind attributing the pulses received from a pulsar to the rotation of an object (neutron star) and emission from the magnetic poles (of the said neutron star), given that fact that pulsars have not been resolved yet in various wavelengths?

Could the pulses have been a product of a non-rotating but radially vibrating radio emitting star?


texts: So is there nothing like satellite anymore?

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I just read this article. I don't know how credible it is, since I couldn't find any link to the original paper. But it says that pluto will be considered a planet again, along with more than 100 other celestial objects including our moon. So, if the definition given here is applied, then would there be anything as dwarf planet or satellite? I think even comets and asteriouds would come under this defintion. I am talking about this:

  The paper, published in Lunar and Planetary Science, declares a planet as a round body that's never undergone fusion, and has less mass than a star. That's it. This means, Pluto would be planet again-- But it would also bring along Ceres, Eris, Makemake and Haumea... as well as 97 other objects.


texts: What does the word "compact" mean in astronomy/astrophysics?

texts: I have seen countless times the adjective "compact" in astronomy, e.g. compact stars, compact binaries, etc. I would like to know, what exactly is this supposed to mean? From this source, I am led to believe that "compact" is meant to denote objects of the greatest matter densities in the universe, i.e. white dwarfs, neutron stars, and black holes. Is this correct?


texts: What is the most mass that matter likely to form?

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If we plot graph between accumulate of forming mass (y-axis) and mass (x-axis), where is the maximum ?

There is a story how I get this question. It start when I think about question "Is our sun is big or small ?".

https://www.quora.com/What-is-the-average-mass-of-a-star

The average mass ends up being around 0.5 solar masses.

But very high mass stars have very short life span so there are more O-type main sequence stars ever form more than O-type main sequence stars we see today.

I think it would be better to measure our sun by using average mass of forming stars than average mass of stars we see.

So, what is average mass of forming stars ?

Then I think a litle bit more. There is no exact boundry between large brown dwarf and small red dwarf stars. So, if we include them too, what is the most mass that matter likely to form ?

If it is inverse-square law, so graph between accumulate mass (y-axis) and mass (x-axis) will be y=c/x where c is constant.

And make the maximum is zero or mean that most of matter aren't form star. At this point, I think I should limit the minimum mass of forming object at some point. But is it inverse-square law for all type of forming object?

If most of matter aren't form star, will be gas cloud. So we don't count them (both molecular gas and mono-atomic gas but dust is still count because it is solid not molecular or mono-atomic object), what is the most mass that matter likely to form?

Please help me or tell me what should read to answer or give keyword to me.


texts: Why is there so little nitrogen in the Martian and Venusian atmospheres?

texts: Why don't our neighbors have much nitrogen?  You would think that, without 'nitrogen-fixing' organisms and such, there might be more.....


texts: Why do astrophysicists often use redshift in plots? Why it is important to know how an astrophysical object evolves in function of redshift? I was seeing an "cosmological time per redshift galaxies formation plot" and thinking why redshift and not, who knows, density?


texts: Is there any real evidence to prove or disprove the existence of alien civilizations?

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Is there any real proof that alien civilizations exist in outer space? What if someone were to say that Earth is the only inhabited planet in the whole universe? How would you respond?

I need to write a five-paragraph argumentative essay to prove that alien civilizations exist. I need to write an introduction, three paragraphs supporting my statement that aliens exist, and a conclusion. In each of the three "body" paragraphs I need to describe in detail a piece of evidence supporting my claim.

I don't even know where to start. I mean, I want to find out the opinion of some scientists who think that we are alone, and then disprove their claim in my essay. I need to know the latest scientific evidence on the existence of alien civilizations. I don't mean like alien abduction stories or any of that science fiction stuff. I need some real proof that will be convincing and not undermine my argument.

How can you know for sure if there are alien civilizations in outer space? What do they look like? On which planets do they live? What kind of technology do they use? Why are we not alone in the universe? What evidence disproves the claims of Earth chauvinists?


texts: Opportunities to see a near earth object via unaided eyes or binoculars?

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I would like to see a near earth object proper with my eyes or binoculars someday.
Has this been possible recently? Are there any upcoming potential opportunities to do so in say the next 20 or 50 years? I have a shot at the first one, the second one is for the benefit of others :-)


texts: How do scientists differentiate between a total and a partial transit of a planet passing in front of its star?

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Say there's a star in our local neighborhood with a Jupiter-sized planet orbiting around it. This planet's orbit happens to lie approximately in our line-of-sight – we can only see a quarter of it transit in front of its star.
All scientists do is look at the amount of starlight blocked during a transit and deduce the size of the planet.
So since this planet only partially transits, are scientists able to tell it's a partial transit and the planet is actually Jupiter-sized? OR are they going to naively assume it's just a smaller planet passing in front of its star?


texts: Icy moons: why hasn't the ice sublimated away?

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Let's take Europa for example:
The predominant model suggests that heat from tidal flexing causes the ocean to remain liquid and drives ice movement similar to plate tectonics.
The heat generated from the tidal flexing has to go somewhere. Is it all carried away by the water vapor plumes we recently detected? Is more water from the ice cover melting away? Is it just radiated away?
I would expect it to cause sublimation as well: There is hardly an atmosphere (molecular oxygen at 0.1 micro Pascals, or 10-12 times that of the Earth), and a tenuous ionosphere.
And that same article suggest that the surface ice is also broken down by radiation:

the oxygen [...] is formed through the process of radiolysis, where ultraviolet radiation from the Jovian magnetosphere collides with the icy surface, splitting water into oxygen and hydrogen. The same radiation also creates collisional ejections of these products from the surface, and the balance of these two processes forms an atmosphere.
The hydrogen, meanwhile, lack the mass needed to be retained as part of the atmosphere and most is lost to space. This escaped hydrogen, along with portions of atomic and molecular oxygen that are ejected, forms a gas torus in the vicinity of Europa's orbit around Jupiter.

Or do we have reason to believe that any losses are compensated by ice being deposited from external sources?


texts: Any pictures showing difference in moon between southern and northern observers?

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Since observers in different parts of Earth will be observing the moon at slightly different angles relative to its (choose reference vector: north pole, origin of latitude longitude position, whatever), they will be observing very slightly different faces of the moon.

I tried looking online to see if anyone had examples of photos of the moon taken from different parts of Earth at the same time but got overwhelmed of photos showing that the moon appears "upside down" in the southern hemisphere relative to what a northern observer would expect and couldn't find any.

Does anyone have or know where to find an example of what I'm asking?  Please note that I am not asking about the "upside down" moon effect I just described, and neither am I asking about lunar libration: I am specifically asking about being able to observe slightly different faces of the moon simply by standing somewhere else on Earth as someone else at the same time.


texts: Does a continuous deformable mirror cause diffuse reflection?

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We have all seen images like this of deformable mirrors:

Continuous deformable mirrors are known to have a higher quality over segmented mirrors, but it seems to me that a continuous mirror (or even a segmented tip tilt mirror) would cause diffuse reflection.  Here is a figure showing a segmented and a continuous mirror

Since the light is coming in normal to the telescope (let's just say space telescope so we can avoid all possible atmospheric non-normal light), the purpose of the deformable mirror is to adjust the phase of the light.  It would appear to me that a continuous deformable mirror would also diffuse the light as seen from my rough drawing (I know that most mirrors are placed at a 45 degree angle, but you get my point).  Here is a figure showing the diffuse reflection at a 45 degree angle.

It is well known that a segmented mirror causes light scatter (at each segmentation location), but I have not been able to find any literature on light diffusion on a continuous deformable mirror.  This must be true, but how is it not a problem and how do they address it? (pointing towards scholarly resources would be appreciated)
UPDATE
I will accept the answer posted below, but I think it is missing something important.  In the fourth bullet it is stated,

I would conjure that the diffusion reflection at segmentation locations is not significant enough compared to the overall sub-mirror reflection

This is still an opinion (though it could be correct), which is why I specifically asked for scholarly resources.
I reached out to Professor Thomas Bifano from Boston University who specializes in deformable mirrors and his answer made sense and was readily verified in scholarly papers

Diffuse reflection occurs when the reflective surface is rough: scale of surface asperities is large in comparison to the wavelength of light reflecting from it. In diffuse reflection, incident light at a fixed angle of incidence reflects (actually, scatters) at many different angles. If the local roughness of the surface is <<wavelength, there no diffuse reflection.


texts: Why does e.g. Hubble's secondary mirror not block part of the picture?

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The SOHO observatory has an opaque object in the light path that blocks the direct light from the sun making it possible to observe the corona.
Hubble and many other telescopes have a big primary mirror in the bottom of a tube which bounces light on to a smaller secondary mirror at the opening of the tube. Why doesn't that other mirror cause a circular area of "no data" in the middle of the resulting images?


texts: Is there a plausible causal mechanism to explain why the Sun would be heating up faster/ sooner than we thought? Question for a novel

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I am writing a novel about what it will be like on earth 500 or so years before the death of our Sun. The Sun is heating up gradually and one day that will negatively affect life on Earth. I know that we are a long ways away from the heat being to much to permit life though. That being said, the novel is more about the social/political/religious ramifications of living in such a time. I still am very interested in making it as relatable and understandable as possible.

Is there any causal mechanism (hypothetically or imaginatively possible) that could cause the sun to heat up faster than it is at present? This could be internal (something collapses and the increase in core pressure speeds up the reaction rate of hydrogen fusion) or external (something impacts the sun with enough extra mass to increase net g, thus increasing pressure in the core).

If not a causal mechanism, maybe something you can think of that current science/ scientists could have missed/ aren't taking into account in their models that, if true, would mean the sun is going to be much hotter, much sooner than we thought.

Thank you so much for your help! I am pretty passionate about writing and I am only an amateur in the subject of astronomy. I'm hoping some brilliant minds can help me flesh out this idea to make it more concrete.


texts: Is there a stellar database that indicates how long ago stars in our Galaxy formed?

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There are several ways of determining the age of a star: its position in the HR diagram, the presence of a protoplanetary disk, it belonging to a cluster...

When did the stars in our Galaxy form? Do we know their age? Does there exists a database of stars for which we know the age, from which this average could be computed ? Is there a histogram of how long ago the stars in our Galaxy formed?

The amount of stars being formed as a function of time is shown for instance in Snaith et al 2014, but this doesn't directly translate into a histogram of the age of the stars currently in our galaxy, since the more massive ones that formed early on are gone.


texts: Is there anything different about the gravitation around a non-spinning black hole and a neutron star of the same mass?

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If we perform a simple experiment by orbiting identical spacecraft around a non-rotating black hole and a non-rotating neutron star of equal mass at a "safe" distance, and ignore differences other than gravitation (e.g. magnetic fields and charge) would there be any differences in their orbits predicted by general relativity?
"Safe" distance means far from the event horizon of the black hole and where tidal forces don't disrupt the spacecraft.
After writing this answer I am now wondering if it's 100% correct.


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Can the eccentricity of a planet's orbit be found just from the analemma of its star? We can draw an analemma given the axial tilt and eccentricity, but how do we find the reverse?
Note: I already know that the highest and lowest points indicate the amount of axial tilt


texts:
Tonight between 4:30 am & 5 am, we were star gazing on a skyscraper. We saw hazy illuminated triangle patch. We took out star app but didn't find any comet passing through that region & I was sure it wasn't Andromeda Galaxy. I'm not sure what I watched.

Please note we thought it could be light of aeroplane, but we were sure it wasn't as it didn't move quickly. The second thought was some form of satellite. I think there isn't any satellite with that much light.

Please can anyone help me identify hazy triangle patch in the sky. I am attaching star map of my sky. The region I saw the hazy patch is marked with red circle on the map.

I'm based out of Mumbai. I don't want my curiosity to die without knowing what I saw, I'm happy to be wrong if it isn't any stellar object. Thank you.


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Is there any information about the future of the neutron star?
What I am interested what happens to it as the time passes. Say a billion years. Would it still be a neutron star? Would it collapse to black hole? Would it simply dissipate?


texts: How many planetary systems exist in our galaxy?

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For many years scientists have studied our own solar system and modern technology allows them to look deeper and deeper into space. Knowing the Sun is only one of a few billion stars in the Milky Way galaxy, I can imagine scientists also started studying other planetary systems… at least enough to know how many planetary systems (like our solar system) reside in our galaxy.

Is there any information available that would be able to (at least "indicate") how many planetary systems reside in our galaxy?


texts: What is the significance of minus sign in the expression of apparent magnitude?

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The apparent magnitude of a distant object in the sky is measured as
m=(-)2.5 log (I/I0)
Where I is the intensity of the object whose apparent magnitude is to be measured and I0 is the reference magnitude. My question is why we put the minus sign in the expression.


texts: Will the SKA's total bandwidth still exceed the Earth's internet's bandwidth?

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In the early 2010's there were many popular articles that said that the total bandwidth of the the Square Kilometer Array's optical fiber network for raw data from each dish would be larger than the Earth's internet. Here is just one example:

Wikipedia's Square Kilometre Array
:

  It would require very high performance central computing engines and long-haul links with a capacity greater than the global Internet traffic as of 2013.3

As you can see that link is broken.

The SKA project has several Precursors, pathfinders and design studies but the SKA proper has not been built yet, and perhaps is not even finalized.

Still, with available data, by the time it might be built (2025?) is it likely to still exceed the Earth's internet's bandwidth?


texts: How to understand Kepler telescope under large aspherical wavefront

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To my understanding, a Kepler telescope is designed to conjugate one plane to another. For example scale down/up the incoming wavefront onto a wavefront sensor for measurement. It works well for small wavefronts, i.e. the wavefront is relatively flat (e.g. $<10 \lambda$ wavefront RMS).

What would happen if a large aspherical wavefront is impinging onto the same Kepler telescope system? Paper Calibration issues with Shack-Hartmann sensors for metrology applications suggests to place the aperture at the shared focal plane for performance improvement, as below:

How to understand the intuition behind? Why would Kepler telescope fail for large aspherical wavefronts?


texts: Could the Universe really be 12.5-13 billion years old?

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My initial reaction is that "this must be wrong" and apparently that's a lot of people's initial reaction according to the article.

https://www.nbcnews.com/mach/science/universe-may-be-billion-years-younger-we-thought-scientists-are-ncna1005541?cid=sm_npd_nn_tw_ma

My question is, is this study actually making scientists scratch their heads, and, 2nd part, if accurate, how could the 13.78 (or whatever it is) estimate have been wrong, as it seemed to be the result of more and more accurate estimates over time.

One of the two estimates has to be wrong.